Destination Science: Caves, Hot springs, and Diamonds in the Ozarks

Arkansas' unique geological history has produced a surprising number of beautiful natural attractions.

ARKANSAS, USA—Arkansas is rarely on anyone’s bucket list. I found myself there only because I was visiting my mother’s family over the Christmas holidays. Then I started exploring—and what a surprise. Had I been a spelunker or a rock hound, I would already have known that Arkansas is blessed with some of the most beautiful and unusual geologic sites in the world. It is a place, asserts Mike Howard, geology supervisor of the Arkansas Geological Survey, where “everywhere you look there’s evidence of just how dynamic the earth has been.” So my family and I decided to visit some of the more remarkable locations in the Natural State.

Two and a half hours north of Little Rock is the most famous science destination in this part of the world, Blanchard Springs Caverns. Back in the Cambrian Era, when the Ozarks were beachfront property, countless marine organisms collected in the shallows of an ancient ocean that would in time become the Gulf of Mexico. Over hundreds of millions of years, those little critters—or more precisely, their calcium-rich shells—were compressed into limestone. This country’s largest living cave system (one within which formations are still growing), the caverns formed when the ancient limestone here became exposed to acidic water. That water gradually corroded the stone, creating a wide variety of speleothem cave formations, rocks made of secondary minerals derived from the original stone. The waters of Blanchard Springs have worked on the caverns for millions of years, and the result is a series of stunning calcium features: dripstone, flowstone, “soda straws,” stalactites, and stalagmites. You can see them in huge caverns—including one the size of three football fields—on the easily accessible Dripstone tour that even my claustrophobic 87-year-old grandmother enjoyed. The Wild Cave tour is for those who want to get dirty, wear cool headlamps, and see some bats.

The Ozark region’s karst topography—a type of landscape shaped by the dissolution of limestone or other soluble rock—has produced a spelunker wonderland. It holds hundreds of wild, commercially undeveloped caves representing a variety of geologic types. The best way to explore them is to hook up with a local “grotto,” or caving club; COBRA (Cavers of the Batesville Region of Arkansas) out of Lyon College in Batesville is one that welcomes both beginners and experienced spelunkers.

After all the cave exploring, our muscles were a bit sore. So in the interest of science we traveled three hours south to the Ouachita range to visit another Arkansas geologic phenomenon, Hot Springs National Park. Here we soaked in spring water warmed by geothermal heat at depths of as much as 8,000 feet; radiocarbon-dating suggests the water may be up to 4,400 years old. The flow from 47 clustered hot springs currently serves two historic spas, the Buckstaff and the Quapaw, both on Bathhouse Row, a collection of architecturally significant structures built early in the last century.

This region is also notable for having perhaps the first mining operation in what is now the United States. Native Americans dug systematically for Arkansas novaculite, a silica-rich mineral used for arrowheads some 10,000 years ago.

It was the day after Christmas, and it was clear that Santa had ignored my wish list and left not a single diamond in my stocking. Hence we headed off to find some diamonds at what may be the most unexpected geologic site in the state, Crater of Diamonds State Park in Murfreesboro, one hour farther south. This 37-acre plowed field is the eighth-largest diamond reserve in the world and the only spot on the planet where you can go prospecting for the gems and keep any that you find. Each year tourists like you and me unearth hundreds of diamonds, including some of the largest and most perfect ever found.

And what exactly are diamonds doing in an Arkansas field? Margi Jenks, park interpreter, explained: Diamonds are remnants of carbon dioxide pockets from when our planet formed. They lie in the earth’s mantle and reach the surface only when carried up via a volcanic pipe. We were actually trudging around the eroded crater of a volcano that erupted about 106 million years ago.

On that cold day in December, there were only a few of us hardy prospectors, several with their “diamond sniffing” dogs. There are three ways to hunt diamonds at the crater. Surface inspection is the most productive after a hard rain exposes the minerals: You simply walk around and look at the ground until something shiny catches your eye. More hard-core diamond hunters can “dry sift” the soil through sifting pans. Recent record rainfall had turned the field into mud, however, so on the day of our visit, anything “dry” was impossible. Instead, we “wet sifted,” placing a hunk of volcanic clay in a sieve and gently washing it in a sluice. The clay dissolves, leaving behind rocks that you can sort through. The famous 3.03-carat Strawn-Wagner diamond—the only diamond ever rated perfect by the American Gem Society—was discovered by this method.

We found what might be an amethyst, some quartz, and…was that a diamond? The staff shook their heads. Apparently we’d just collected a bunch of pretty rocks. At least we got to play in volcanic mud. Maybe you’ll have better luck. Admission to the search area is $7, and renting sifting pans and shovels runs about $9.

Oil you need to know

Geology buffs and those interested in quirky but fascinating museums will not want to miss the Arkansas Museum of Natural Resources in Smackover. In 1922 one of the most dramatic oil discoveries in history took place here. The Smackover formation, a 65-square-mile Jurassic oil field, was for a few years the nation’s largest oil-producing facility. Now it is home to this little gem of a museum. Built and maintained by a special state tax on extractive industries, it is an extremely well-funded facility with indoor and working outdoor exhibits tracing the history of Arkansas’ natural resources. While it pays lip service to things like timber, the museum focuses primarily on petroleum and bromine, more of which is produced in Arkansas than anywhere else in the world. Kids will love the “center of the earth” corridor, a circular hall that takes you from the crust all the way to the core.